1. Technical Field to which the Invention Belongs
The present invention relates to a motion picture code evaluator and in particular to a motion picture code communications evaluation technology to evaluate the code and the protocol used in transmission/reception of digital motion picture data.
2. Prior Art
A digital motion picture is a continuous sequence of instantaneous pictures in time called motion picture frames (hereinafter referred to as frames).
Data of a digital motion picture is generally huge. Thus, motion picture code transmission is generally performed where compression or encoding of information is made for data communications, followed by a decoding process to regenerate a motion picture.
Standards for motion picture codes includes, for example, MPEG (Moving Picture Experts Group)-2 (ISO/IEC13818) and MPEG-4 (ISO/IEC14496) specified by ISO/IEC (International Organization for Standardization/International Electrotechnical Commission), and H.261 and H.263 specified by ITU (International Telecommunication Union) recommendations.
The present invention is applicable to similar motion picture codes as well as the international standards.
In the aforementioned motion picture code, frames comprise pixels arranged in a shape of a grating. A frame has a format such as the CIF format comprising 352 pixels in the horizontal direction and 288 pixels in the vertical direction and the QCIF format 176 pixels in the horizontal direction and 144 pixels in the vertical direction.
The number of pixels which constitute a frame is also called a screen size.
In the case of a color image, the number of pixels available in the CIF format are a luminance screen (Y) and a color difference screen (U, V). A 4:2:0 format which assigns one pixel to U information on the color difference screen and one pixel to V information on the color difference screen per two by two pixels on the luminance screen, and a 4:2:2 format which assigns one pixel to U information on the color difference screen and one pixel to V information on the color difference screen per two pixels on the luminance screen are available.
The number of pixels on the color difference screen in the 4:2:2 format is double that in the 4:2:0 format.
The primary colors, RGB (red, green, blue), may be used to represent respective number of pixels.
The number of pixels indicates luminance and color difference or all pixels of the primary colors.
It goes without saying that the more the number of pixels per frame is, the higher-resolution or higher-quality picture is obtained.
The number of frames per unit time may be 30 frames per second or 15 frames per second. The greater this figure is, the smoother motion is represented, that is, the higher-quality picture is obtained.
In digital representation of luminance, intermediate halftones from the darkest black to the lightest white are quantized.
In such a case, the quantization level represented by a digital value is finite. In general applications, levels in the neighborhood of 256-level gray scale which can be visually represented in eight bits are used.
The number of colors is infinite when colors are digitally represented. Colors around 16 million colors are used.
Such colors may be the number if levels of gray scale quantization.
The number of quantization levels is the number of colors unless otherwise specified.
In this case also, the more the number of gray-scale levels is, the higher-quality picture is obtained.
The total number of quantization levels gathered for the pixels in all the frames within a specific time is called motion picture information amount.
In general, the number of pixels of a frame and the number of frames per second are constant, although there are cases where the number of pixels or frames varies.
The number of quantization levels may vary within a frame.
In terms of a load on a transmission path, transmitter or receiver, the smaller the amount of motion picture codes is, the smaller the load is.
Thus, a higher amount of motion picture codes for the information amount of a picture before compression of information, that is, a higher compression rate or coding is desirable.
In a motion picture code according to the international standards or equivalent, the actual coding efficiency is limited. To reduce a load on a transmission path, transmitter or receiver, it is practically efficient to reduce the number of pixels, frames, and quantization levels. This degrades the picture quality.
Actual operation in transmission of motion pictures is costly. Thus, a service method is available which charges by the amount of information in motion pictures, in order to compensate for a load on a transmission path, transmitter or receiver.
Quality degradation of a motion picture in the course of transmission of a motion picture code will be described.
In communications of a motion picture code, the receiving party obtains a lower quality picture than the original for the following reasons:
A transmission error may prevent a motion picture code from being properly received.
Some packets may be lost halfway as a result of data transmission in packets.
Communications of motion picture codes may take excessive time. An encoded motion picture frame may not be ready for display at the timing of the display in the ongoing motion picture playback. In this case, display of the motion picture frame is skipped to shift to the processing of the next motion picture frame.
In this way, a section which failed to display an encoded picture of the original motion picture is called a loss of motion picture.
A transmission error has different affects on the decoded motion picture to be displayed, depending on the section where the error has taken place.
A section which accommodates parameters to represent the specifications for the entire motion picture codes such as the screen size of a motion picture code and a color difference format as well as codes used in the predictive coding system and prediction method for the entire frame is called a header.
In case a transmission error has occurred in the header section, display of the entire decoded motion picture may be disabled or display of the entire decoded frame may be disabled.
In case a transmission error has occurred in a section concerning the gray-scale level of pixels in a frame, display of the decoded pixel may be disabled.
In this way, the amount of motion picture codes not used for display of decoded pictures due to a transmission error and a delay and the amount of loss of a decoded motion picture are not in a fixed relationship. Thus, a loss of the motion picture must be evaluated on demand.
The example of reference by the same inventor, US-2002-0097803-A1 xe2x80x9cMethod for evaluating dynamic image code communications, and apparatus for evaluating the samexe2x80x9d provides apparatus to evaluate the motion picture information amount and motion picture loss amount.
A configuration example thereof will be described using FIG. 2.
A motion picture code transmitter 11 transmits a motion picture code, which is received and recoded by a motion picture code receiver 22.
The amount of motion picture codes is counted on a motion picture code counter 27.
A motion picture loss evaluator 33 evaluates a motion picture loss amount as described below.
A motion picture quality evaluation value converter 38 subtracts the motion picture loss amount from the motion picture information amount.
The principle configuration and operation of the aforementioned motion picture loss evaluator 33, which is described in the Japanese Patent Application No. 153078/1999 xe2x80x9cMotion picture communications quality determination apparatusxe2x80x9d will be outlined below.
The motion picture loss evaluator 33 decodes the motion picture codes then records accurately decoded areas and estimates non-recorded areas as losses.
Problems that the Invention is to Solve
In case a service is provided where transmission of a motion picture code in the CIF format is switched to transmission of a motion picture code in the QCIF format in accordance with congestion of the transmission path and degradation of the transmission error rate, quality of the motion picture is roughly divided into two phases.
CIF and QCIR respectively have the CIF format comprising 352 pixels in the horizontal direction and 288 pixels in the vertical direction and QCIF format comprising 176 pixels in the horizontal direction and 144 pixels in the vertical direction. Thus there is a fourfold difference in motion picture information amount between CIF and QCIF.
When a motion picture loss of some percent occurs due to a transmission error, the difference in motion picture information amount between CIF and QCIF falls in the range of about 3.8 to 4.2 times.
Even in case charging is made in proportion to an accurately transmitted motion picture information amount, the number of pixels and frames, (that is, in which format the motion picture was transmitted) greatly affects the accurate motion picture information amount. A motion picture loss of some percent affects the accurately transmitted information amount only as much as one tenth of the difference in the format, as mentioned earlier.
In a related art motion picture code evaluator, a motion picture loss is determined on a pixel basis so that a received motion picture code is decoded.
In this case, the loss amount is calculated to a definition of 0.002% even in case one frame comprises 50,000 pixels.
Pixel-based motion picture loss does not greatly affect the motion picture information amount. Thus a definition of several percent will suffice as mentioned earlier. Nonetheless, in practice, all pixels are decoded to determine any loss, which process is an excessive burden on a receiver.
Under the current situation where transmission technology is fast-evolving, transmission capacity is increasing with the motion picture code rate ever expanding, it is critical to reduce the processing load especially on a receiver.
The object of the invention is to provide a motion picture code evaluator for evaluating the receiving state of a motion picture code with a smaller processing load without decoding the motion picture code, by determining presence/absence of an error in a frame header of the motion picture code and extracting a motion picture coding parameter contained in the frame header.
Means for Solving the Problems
In order to solve the problems, the invention provides, in a first aspect, a motion picture code evaluator for evaluating, on a motion picture receiver for receiving a motion picture code via transmission means and decoding the received motion picture code, the transmitted motion picture information amount which is based on losses of a motion picture caused by the transmission means, the motion picture code evaluator comprising means for testing the frame header of the motion picture code and determining the presence/absence of an error in the frame header to calculate the frame loss ratio per predetermined time, means for extracting a motion picture coding parameter contained in the frame header and detecting a variation in the motion picture coding parameter in the predetermined time, and means for summing the motion picture coding parameter and the motion picture coding parameter weighted by the variation in motion picture coding parameter in the predetermined time to calculate an ideal motion picture information amount in a predetermined time, characterized in that the motion picture code evaluator thereby obtains an actual motion picture information amount by multiplying the ideal motion picture information amount by (1-frame loss ratio).
In a second aspect of the invention, the motion picture coding parameter includes the number of motion picture code pixels, frame rate and number of quantization levels, and the means for detecting a variation in the motion picture coding parameter in the predetermined time detects the ratio of frames where the values of the number of pixels, frame rate and number of quantization levels remain the same, to the predetermined time.
In a third aspect of the invention, the values of the number of pixels, frame rate and number of quantization levels contained in the frame header where an error is detected are neglected and the values of the number of pixels, frame rate and number of quantization levels in the immediately preceding header are assumed as valid.
In a fourth aspect of the invention, the number of quantization levels in the header of the layers lower than the frame in addition to the number of quantization levels contained in the frame header is extracted as the number of quantization levels.
In a fifth aspect of the invention, the means for detecting a variation in the motion picture coding parameter in the predetermined time is a timer or a counter reset when a parameter different from one contained in the immediately preceding frame header is detected.
The invention, in a sixth aspect, provides a motion picture code transmission network which outputs a frame loss ratio according to any one of the first through fifth aspects to network management apparatus for managing transmission of a motion picture code to modify, at the sending party, at least one of the parameters including the screen size of a motion picture code, color difference format, frame rate and number of quantization levels.
The invention, in a seventh aspect, provides a billing system for a motion picture transmission service which charges depending on the receiving quality of a motion picture by outputting the actual motion picture information amount according to anyone of the first through fifth aspects to billing means.